Scalable Quantum Light Source Enables Quantum Cryptography, Computing

Photonics SpectraJan 2019
Researchers at Stevens Institute of Technology and Columbia University have developed a scalable, precise method for creating large numbers of quantum light sources on a chip. These light sources could be used for quantum computers and quantum cryptographic systems. The researchers said that the method combines spatial control and scalability with the ability to efficiently emit photons on demand.

Researchers have created a scalable platform for on-chip quantum emitters. Courtesy of Stevens Institute of Technology.
The researchers used the corners of a metal nanocube for both electric field enhancement and to deform a 2D material. This nanoplasmonic platform allowed them to study the same quantum emitter before and after coupling.

The Columbia team developed a technique for growing nearly defect-free crystals. The researchers used the crystals to build rows of quantum emitters. To create the emitters, an atom-thin film of semiconducting material was stretched over a nanocube made of gold. As the film was stretched over the corners of the cube, it left an imprint of defined locations where single-photon emitters formed.

In addition to imprinting the quantum emitter on the chip, the gold nanocube acted as an optical antenna around it. To form the nanoantennas, the researchers attached a mirror to the bottom side of the nanocube. The quantum emitters were created in the space between the gold nanocube and the mirror, leaving a narrow gap only 5 nm in size.

“This tiny space between the mirror and nanocube creates an optical antenna that funnels all the photons into that five-nanometer gap, thereby concentrating all the energy,” said Stevens Institute professor Stefan Strauf. “Essentially, it provides the necessary boost for the single photons to be emitted rapidly from the defined location and in the desired direction.”

A new, efficient method for creating nanoscale light sources could be used in quantum computing and quantum cryptography. Courtesy of Stevens Institute of Technology.For a 3 × 4 array of quantum emitters, the researchers demonstrated Purcell factors of up to 551; single-photon emission rates of up to 42 MHz; and a narrow exciton linewidth as low as 55 μeV. According to the researchers, the firing of 42 million single photons per second is a new record. Using the new method, every second trigger created a photon on demand, compared to one in every 100 triggers previously.

Though tiny, the emitters are remarkably tough. “They’re astonishingly stable. We can cool them and warm them and disassemble the resonator and reassemble it, and they still work,” Strauf said. Most quantum emitters must be kept chilled to −273 °C, but the new technology works up to −70 °C. “We’re not yet at room temperature, but current experiments show that it’s feasible to get there,” Strauf said.